Magnetic recording media are generally composed of a magnetic layer containing a ferromagnetic powder and a binder as main components. The magnetic layer is coated on a non-magnetic support such as polyethylene terephthalate film, polycarbonate film or polyimide film.
The ferromagnetic powders used are iron oxide powders and metal powders. The metal powders are used to increase the magnetic recording density and output level and provide more saturation magnetization and coercivity.
The so-called "metal tape" magnetic recording media have been practically researched particularly with respect to video recording systems because they have higher recording density than that of iron oxide recording tapes. For example, small VTR systems which are associated with a camera have been proposed and the metal tape is employed in the systems, which require two or more times the recording density required of VHS systems and .beta.-systems, a half diameter of head cylinder and a half relative speed of head/tape less than the present systems. Accordingly, the recording wave length is half that of present tapes which appears to be about 0.6.mu. to about 1.mu..
In such new systems, recording and reproducing images of the same or better quality than those of present systems are required under the above conditions. Therefore, the C/N ratio of magnetic recording medium in the new systems must be not less than 6 dB which is higher than that of magnetic recording medium in the VHS/.beta.-systems where they are evaluated under the same conditions. The C/N ratio means a ratio of output level of the reproducing signal to the modulation noise when a FM carrier wave is recorded.
A magnetic recording medium must satisfy various conditions in order to achieve the above requirements, and must also eliminate various problems.
Because the recording density is higher and the recording wave length (.lambda.) is shorter, the spacing loss that is the clearance (g) between the tape and head should preferably be smaller. Therefore, it is preferred if the magnetic layer has improved surface properties. However, if the surface properties are better and hence the magnetic layer has a smooth surface, the tape can not stably run because due to high contact resistance with the guiding rolls of a VTR apparatus, or resistance with the head cylinder and devices in the cassette. The unstable running property of tapes decreases the image quality and makes the tape abrasive which causes problems in the durability of tapes.
The output level in short wave length recording has no spacing loss problems due to the use of ferromagnetic metal powder. It is necessary not to simultaneously increase the noise in order to guarantee the image quality of reproduced images. A magnetic layer having better surface properties or a smooth surface is more advantageous to decrease noise, and uniform dispersion of ferromagnetic powders is important to the surface property.
A magnetic layer having better surface properties, stable running properties and better durability is necessary to obtain metal tapes having better video characteristics in high recording density using a recording wave length of not more than 1.mu.. Therefore, novel technics other than VHS and .beta.-type iron oxide magnetic recording tapes are needed to develop magnetic recording tapes satisfying the above conditions.